Most breeders have their cats in projects and partnered so I don't think this is something a breeder doesn't want to help you with but their cats are simply occupied.
Welcome to KittyCatS by the way
If I have a single cat which I need to breed for some reason such as testing it's hidden features I go to a "Love Shack" as Nen mentioned as well.
Breeders offer there cats for sale which are (almost) ready to breed.
You can find these for example at the "Simply Too Adorable" sim.